METAL-ION-PROMOTED HYDROLYSIS OF POLYURIDYLIC ACID

First-order rate constants for the hydrolysis of polyuridylic acid in the absence and presence of various metal ions and their chelates have been determined under neutral and slightly acidic conditions. The hyd rolysis has been shown to proceed by cleavage of non-terminal bonds ra ther han by stepwise release of monomeric nucleotides. Only the hydrol ysis of the 3',5'-phosphodiester bonds is accelerated by metal ions, n ot their isomerization to 2',5'-bonds. The catalytically active specie s has been shown to be the monohydroxo form of the metal aquo ion. The rate accelerations are parallel, but up to 20 times greater than thos e obtained with uridylyl(2',5') uridine. The mechanism of the metal-io n action is discussed.